Soil morphology-Peoria loess grain size relationships, southeastern Minnesota

Soil profiles formed in Peoria Loess in southeastern Minnesota allow further examination of the widely observed morphological variation of loess-derived soils with distance from the loess source. In these profiles, morphological variables representing depth of clay accumulation and solum thickness decrease with increasing ratios of coarse silt to total silt in the loessial parent material (R² = 0.297-0.772). Variables representing depth of clay accumulation also decrease with increasing parent material carbonate content (R² = 0.297-0.585), but the relationship is weaker. Clay accumulation depth increases with increasing parent material clay content, but the relationship is very weak (R² = 0.044-0.102). The observed relationship between a grain size and clay accumulation, is consistent across a wide range of organic matter accumulation, although Typic and Mollic Hapludalfs tend to have shallower clay maxima than darker colored Mollisols. In this study area, unlike other regions of the midwestern USA. Stronger soil development in the finer loess cannot be attributed to a shallow, perched water table. We hypothesize that abrupt downward increases in grain size at coarse loess sites inhibit downward moisture flux and, over the long term, limit both the depth of soil development and the amount of weathering and clay accumulation.